1. Field of the Invention
The present invention relates to a thin film magnetic head, which has its recording and reproducing efficiency improved, and a fabricating method thereof, and more particularly to an inductive thin film magnetic head, which has its signal input and output coil improved, and a fabricating method thereof.
2. Description of the Prior Art
A thin film magnetic head according to the prior art is constructed, as shown in section by way of example in FIG. 1, of: second and first magnetic poles 2 and 1 over a magnetically insulative substrate 6; an insulating layer 3 for electrically and magnetically isolating the first and second magnetic poles 1 and 2; and a conductor 4 disposed in the insulating layer 3 to form a signal input and output coil. Incidentally, as the case may be, a magnetic substrate such as Mn--Zn ferrite may be used to act as the second magnetic pole, or a suitable insulating or metal layer is interposed so as to improve the electric insulativeness the contact and so on. By impressing a signal voltage upon the conductor 4, a leak magnetic flux to pass through a magnetic recording medium 5 is established in the gap between the first and second magnetic poles 1 and 2 (i.e., the operation gap) at the front (i.e., the side facing the magnetic recording medium) of the magnetic head, thus effecting the recording operation. On the other hand, the reproduced output is made to appear as an output voltage at the conductor 4 by the so-called "electromagnetic induction" resulting from that the magnetic flux generated by the recording medium 5 passes through the first and second magnetic poles 1 and 2. It is, therefore, conceivable that the signal recording and reproducing operations can be facilitated the more as the number of turns of the coil formed by the conductor 4 is increased the more. As a matter of fact, however, if that number is merely increased, the magnetic circuit is augmented to increase the magnetic resistance so that the efficiency is not always improved. In order to improve the efficiency, it is necessary to wind the coil a number of turns densely as close to the front of the magnetic head as possible. In order to increase the recording current, on the other hand, it is necessary to enlarge the effective sectional area of the conductor. In short, the contradictory problems that the sectional area of the conductor is enlarged in a limited region and that the number of the conductor 4, i.e., the coil is enlarged have to be solved. The method of forming the conductor 4 according to the prior art will be described in the following.
FIGS. 2a to 2d show an example for forming a conductor coil by the wet etching treatment. For simplicity of explanation, only the process of forming the coil will be described. As shown in FIG. 2a, a substrate 8 is coated with an aluminum layer 7 as the conductor, on which a resist pattern 9 is formed by the photo-etching treatment, as shown in FIG. 2b. After that, the Al layer 7 is etched with an etching liquid such as phosphoric acid to form the conductor layer 4, as shown in FIG. 2c. At this time, by the wet etching treatment, an undercut d.sub.0 is established below the resist pattern 9, as shown in FIG. 2c, to reduce the sectional area of the conductor 4. On the other hand, since the undercut d.sub.0 becomes the larger with the increase in the thickness t of the Al layer 7, it is limited to reduce the width d.sub.1 of the conductor 4 and to increase the number of turns, and it is difficult to increase the thickness t thereby to augment the sectional area. The results of the experiments conducted by us, the inventors, have revealed that the undercut d.sub.0 is substantially equal to t in case the thickness is small (t&lt;d.sub.1). Even if a conductor pattern having a large thickness (t&gt;d.sub.1) is to be formed, not only the undercut is further enlarged to a remarkable extend but also the conductor itself is remarkably thinned. As a result, the photoresist pattern may be separated during the etching treatment so that the desired conductor pattern can not be formed in fact. If the Al layer has a thickness of 2 .mu.m, for example, the width d.sub.1 of the conductor 4 is limited by about 5 .mu.m. FIG. 2d shows the state in which the photo-resist pattern 9 is removed to expose the conductor 4 to the outside so that the formation of the coil is finished.
On the contrary, the reactive sputter etching treatment has been found to provide a working treatment having less undercut d.sub.0. FIGS. 3a to 3e show the etching process. As shown in FIG. 3a, the substrate 8 is coated with the Al layer 7, for example, on which the resist pattern 9 is formed, as shown in FIG. 3b. After that, the Al layer 7 is worked by the reactive sputter etching treatment in the atmosphere of a BCl.sub.3 gas. During the reactive sputter etching treatment, as shown in FIG. 3c, not only the Al layer but also the resist layer are etched so that the film thickness is gradually decreased. When the etching treatment of the Al layer is finished, the resist has to be still left. This state is shown in FIG. 3d. After that, if the resist layer is removed, as shown in FIG. 3e, the conductor 4 having less undercut can be formed. Therefore, the reactive sputter etching treatment is a working treatment which can form the conductor 4 having a large sectional area more easily than the foregoing wet etching treatment. For example, if a positive resist pattern 9 having a thickness of 2 to 3 .mu.m is used, an Al layer 7 having a thickness of 4 .mu.m can be worked with substantial fidelity to the resist pattern 9. However, if the thickness of the resist is made larger than 2 to 3 .mu.m, a fine working treatment becomes difficult during the formation of the resist pattern 9 so that the pattern width d.sub.4 and the pattern gap d.sub.3 shown in FIG. 3b cannot be reduced. On the other hand, if the thickness h of the Al layer 7 is larger than the resist pattern gap d.sub.3 (i.e., h&gt;d.sub.3), it becomes difficult to etch the deep portion of the Al layer 7. In other words, the reactive sputter etching treatment is more effective than the wet etching treatment but finds it difficult to form the conductor 4 which has such a thickness as is defined by h&gt;d.sub.1 and h&gt;d.sub.2, for example, h&gt;5 .mu.m, d.sub.1 &lt;3 .mu.m and d.sub.2 &lt;3 .mu.m.
By the reasons thus far described, there have been practised in the thin film magnetic head of the prior art the methods by which the coil conductor 4 is composed of two and three layers in order to prevent the magnetic circuit from being increased as a result that the width d.sub.1 of the coil conductor 4 is enlarged to augment the sectional area. However, those methods are not industrially desirable because they have an increased number of steps and a lowered yield.
The following references are cited to show the state of the art: (i) Japanese Patent Laid-Open No. 55-84019; (ii) Japanese Patent Laid-Open No. 55-84020; and (iii) Japanese Patent Laid-Open No. 55-12522.